As part of treating patients, and more importantly patients that are critically ill, medical professionals evaluate and address patients' hemodynamics. One of the measurements that is useful to medical professionals in evaluating a patient's hemodynamics is central venous pressure (CVP), which is the blood pressure in the thoracic vena cava near the right atrium of a patient's heart. Since the CVP is essentially the same as the right atrial pressure, CVP is an important clinical measurement of the right ventricle's filling pressure. This filling pressure determines the preload of the right ventricle, which directly impacts stroke volume through the Frank-Starling mechanism. A standard first order model predicts that a change in CVP is equal to a change in volume divided by a change in venous compliance. To this extent, CVP is increased by venous blood volume or by an increase in venous tone. Such increases in CVP can indicate hypervolemia, heart failure, or respiratory problems for a patient.
Conventional techniques for measuring CVP are not without their drawbacks, however. Some conventional techniques for measuring CVP are invasive, for example, and involve inserting a catheter into the subclavian or internal jugular vein with a tip positioned in the vena cava just before the right atrium. While this invasive testing can exactly measure a person's CVP, doing so is expensive and involves significant trauma and stress on the person. On the other hand, noninvasive techniques for measuring CVP are inconsistent due to variations in the skill level and techniques across medical professionals. Generally, noninvasive CVP measurement requires the medical professional to visually estimate a peak height of pulsatile waves (rise of blood observable through pulsatile motion) in a person's external or internal jugular vein, and then to measure this height against the person's sternal angle. Such techniques are inconsistent because they rely on a difficult-to-make visual estimate, made by a particular medical professional, as to where the pulsatile wave ends and the height based on the sternal angle. Further, to make these measurements, medical professionals undergo a significant degree of training. As such, they are performed almost solely by skilled physicians, making their use outside a clinic or hospital environment cost prohibitive. The drawbacks of both the invasive and non-invasive CVP-measuring techniques render them less than ideal in many cases.